Chlorine is commonly used in aqueous systems for controlling the growth of microorganisms. For example, in papermaking processes, chlorine is a preferred halogen biocide due to its low cost, broad spectrum and fast biocidal activity, and convenience of monitoring and control. However, use of chlorine also results in increased corrosion of system components, degradation of felts, destruction of other water treatment additives, and negative impacts on paper-making additives such as dyes and brighteners.
To improve the biocidal properties of chlorine, particularly against biofilm and filamentous organisms, and to decrease the negative impact of chlorine use, free chlorine can be stabilized using nitrogenous compounds to form chloramines. Chloramine formation and chloramine's properties as a disinfectant have been known since the early 1900's, and the relative reaction rates of chlorine with amine-containing compounds versus ammonia were studied more that 50 years ago (Weil, I. and J. C. Morris. 1949. “Kinetic Studies on the Chloramines. The Rates of Formation of Monochloramine, N-Chlormethylamine and N-Chlordimethylamine.” J. Amer. Chem. Soc. 71:1664). Chloramines are also approved and widely used for potable water distribution systems (United States Environmental Protection Agency. 1999. Alternative Oxidants and Disinfectants Manual, Chapter 6. EPA publication number 815-R-99-014).
The use of ammonium salts as practical compositions for stabilizing chlorine has also been known for many years. For example, Beck (J. Beck et al., Aqua I, 25-33, 1986) describes the use of pre-formed monochloramine for the post-disinfection of drinking water. In this work, chloramines are formed by mixing ammonium sulfate and hypochlorite solution at a concentration of 1000 ppm and adjusting the pH to 7.5 before the point of dosage to avoid carbonate precipitation. This is typical of chloramines applications, in which the usual ammonium ion sources are ammonia, ammonium chloride and ammonium sulfate.
Additional examples of using chloramines to control biofouling include U.S. Pat. No. 4,988,444, which describes the use of chloramines to prevent microbial fouling on reverse osmosis membranes, U.S. Pat. No. 6,773,607 which describes using chloramine formed in ballast water by adding aqueous ammonia or an ammonium salt, and sodium or calcium hypochlorite to the ballast water and U.S. Pat. Nos. 5,976,386, 6,132,628, 6,478,973 and 7,067,063, and references cited therein which disclose mixing an oxidant, preferably an active chlorine donor and still more preferably sodium hypochlorite and an ammonium salt, preferably chosen among halides, sulfates and nitrates, and adding the biocidal concentrate immediately to the aqueous system to be treated.